Edge case, low priority, but odd enough that it caught my eye so I'm documenting it while it's fresh in my mind. Most of this I have not been able to test or reproduce, so I'll just post some examples and guess at what's going on... Exceptions noted.

2009-08-30 19:18:01Z: closed and migrated; first and second answers deleted

2009-08-30 19:20:10Z: first answer undeleted by author

2009-08-30 19:19:20Z: third answer posted

Both the first and second answers remain visible and fully-unlocked. Primary anomaly: author able to undelete second answer.

Theory:

If I understand correctly, there's a grace period for posting to closed questions, intended to avoid losing the work of authors who are busy composing their answers when a question is closed. That explains #1, but not #2... unless the grace period has been extended to > 23 minutes. #3 i can verify - it's possible for authors to undelete their own answers on migrated questions.

Suggestions:

Normally, there's a good reason for the grace period (if that's what's really going on here): it avoids wasting authors' time when closing is controversial and the question ends up being re-opened anyway. In the case of migration however, "re-opening" is a much less likely (requires moderator intervention) - it would make more sense to just redirect them to the migrated question and ask that they respond there.

I don't think allowing authors to undelete answers on migrated questions really makes much sense; otherwise, why delete them in the first place? They should be locked.